There have heretofore been proposed various zoom lenses having a function to correct image blurs due to hand jiggling when capturing images with cameras.
For example, zoom lenses disclosed in Patent Document 1 and Patent Document 2 have a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power, which lens groups are arranged successively from the object side. At least the second lens group and the fourth lens group are moved along the optical axis for variable power, and the third lens group that is positioned near the aperture diaphragm is moved in its entirety in a direction perpendicular to the optical axis for correcting image blurs at the time the zoom lens is vibrated.
A zoom lens disclosed in Patent Document 3 has a plurality of lens groups. Those lens groups which are movable along the optical axis for variable power or focusing are shifted in a direction perpendicular to the optical axis for correcting image blurs at the time the zoom lens is vibrated.
A zoom lens disclosed in Patent Document 4 has a plurality of lens groups. The first lens group that is positioned most closely to the object side is shifted in a direction perpendicular to the optical axis for correcting image blurs at the time the zoom lens is vibrated.
A zoom lens disclosed in Patent Document 5 has a plurality of lens groups. The final lens group that is positioned most closely to the image side is shifted in a direction perpendicular to the optical axis for correcting image blurs at the time the zoom lens is vibrated.
Optical systems of recent years which have greatly been reduced in size have a highly reduced number of lenses and are made up of small-diameter lens groups. Therefore, manufacturing tolerances and assembling positional accuracies required for the individual lenses are highly stringent, so that skilled manufacturing techniques are needed to achieve sufficient optical performance. For shifting lens groups of such small-size optical systems in a direction perpendicular to the optical axis for correcting image blurs, the lens groups are required to be shifted quickly and accurately in the direction perpendicular to the optical axis. To handle positional deviations along the optical axis, some schemes need to be incorporated to reduce focusing sensitivity.
A review of the conventional zoom lenses indicates that efforts are made in many zoom lenses to reduce an off-center aberration which occurs when a lens group is shifted in a direction perpendicular to the optical axis. For example, a zoom lens disclosed in Patent Document 6 has a hand-jiggling correcting group which is shifted in a direction perpendicular to the optical axis for correcting hand jiggling, and a lens group which is positioned more closely to the image side than the hand-jiggling correcting group and which is fixed upon hand jiggling. Of the lenses of the hand-jiggling correcting group, a lens which is positioned most closely to the image side is referred to as a lens GS, and a lens which is positioned adjacent to the lens GS on the image side and which is fixed for correcting image blurs is referred to as a lens GR. Conditional equations are given about shape factors and refractive powers of the lens GS and the lens GR. These conditional equations are designed to reduce an off-center aberration. Measures that could have been taken from the stage of designing zoom lenses capable of correcting image blurs have not been taken about how to reduce the effect of an off-center component which does not contribute to the correction of image blurs in directions other than the direction perpendicular to the optical axis.
In the zoom lenses disclosed in Patent Document 1 and Patent Document 2, the lens group which is positioned near the aperture diaphragm and which is fixed for varying power is used to correct image blurs. Since an aperture diaphragm mechanism and a vibration insulation actuating mechanism would tend to interfere with each other, the optical system cannot sufficiently be reduced in size.
The zoom lens disclosed in Patent Document 3 has a complex actuating mechanism because vibrations are isolated by the lens groups which are movable along the optical axis for variable power or focusing.
In the zoom lens disclosed in Patent Document 4, the first lens group positioned most closely to the object side serves to isolate vibrations. However, since the first lens group is spaced apart from the image plane and off-axis rays pass through the first lens group off the optical axis, the lens diameter of the first lens group is large, and the vibration insulation actuating mechanism is large in size, which is not preferable.
The zoom lens disclosed in Patent Document 5 has a plurality of lens groups. The final lens group that is positioned most closely to the image side is shifted in its entirety in a direction perpendicular to the optical axis for correcting image blurs at the time the zoom lens is vibrated. However, when the final lens group is shifted in its entirety in the direction perpendicular to the optical axis, it is inevitably positionally deviated along the optical axis to move the image plane, tending to cause defocusing.    [Patent Document 1] Japanese Patent Laid-Open No. Hei 13-124992    [Patent Document 2] Japanese Patent Laid-Open No. Hei 13-356270    [Patent Document 3] Japanese Patent Laid-Open No. Hei 11-282038    [Patent Document 4] Japanese Patent Laid-Open No. Hei 1-189621    [Patent Document 5] Japanese Patent Laid-Open No. Hei 1-191113    [Patent Document 6] Japanese Patent Laid-Open No. Hei 9-230236.